The present invention relates to a circuit configuration intended for a brake system with anti-lock control and/or traction slip control and serving to improve the control during cornering. A circuit configuration of this type includes sensors for measuring the wheel rotational behavior and electronic circuits for conditioning and assessing the sensor signals as well as for generating braking pressure control signals, wherein the braking pressure is controllable in dependence on the wheel rotational behavior, the vehicle speed or a vehicle reference speed as well as on deceleration thresholds, acceleration thresholds and slip thresholds.
The benefit of an anti-lock system is decisively determined by the quality and the precision of braking pressure control and by this control adapting to the various driving situations, to the condition of the road surface and, respectively, to the instantaneous frictional value between the individual wheels and the road surface. As a result, the control must be devised such that, on the one hand, locking of the wheels is prevented and driving stability and steerability are thereby preserved and that, on the other hand, the stopping distance is minimized to the maximum possible extent. The realization of these demands, in part, leads to contradictory measures because, for example, the driving stability is favored by a freely running or relatively weakly braked wheel, while a short stopping distance can only be obtained by a high amount of brake force. Therefore, the control must be adjusted individually for the single wheels as precisely as possible to a value at which the wheel still runs stably, yet also produces a great brake effect. This can be achieved only if the control unit interprets the rotational behavior of the wheels correctly in every situation and can adapt the pressure variation accordingly.
When the information for controlling the braking pressure is obtained merely by means of wheel sensors, there is need for special measures to detect that a specific rotational behavior is caused by cornering or by an imminent locking of any one wheel. This is because the transversely running wheels fake a slip to the control unit during cornering which, when braking is actually performed, signals prematurely a beginning instability of the wheel. The control of the wheel on the inside of a bend is so-to-speak "biassed" thereby towards the detection of an instability of this wheel, the result being that the braking pressure increase on this wheel is stopped prematurely or, respectively, the braking pressure is decreased prematurely and is kept at too low a value; consequently, insufficient braking forces are applied to the wheel. These effects are increased upon brake circuit failure.
Thus, a number of measures are known to identify cornering and to adapt the control to this condition. The International Patent Application WO 90/09301 teaches a circuit configuration of the above-mentioned type wherein, for the cornering identification, at first a lateral reference speed is formed for each vehicle side, and a difference signal is derived from both lateral reference speeds which, after being combined with the vehicle reference speed, can be assessed for the cornering identification and for adaption of the control to the vehicle behavior during cornering.